Based on the summarization and classification on different kinds of phase shift extraction algorithms in generalized phase-shifting interferometry (GPSI), an evaluation and comparing method for these GPSI algorithms is proposed according to experimental detectable amount. Based on off-axis digital holography, by using the residual of direct current (DC) term and conjugate image in reconstructed wave field as criterion, GPSI algorithms can then be evaluated and compared by defining the signal-to-noise ratio (SNR) in reconstructed wave field. Theoretical analysis and computer simulation experiment have proven that the bigger the SNR is, the little the residual of DC term and conjuage image is and the more accurate the extracted phase shift is. Six typical algorithms are compared in simulation and optical experiment and the results are consistent, which verify the feasibility and validity of this method.